Reactance tube modulation



April 77,1942. M. G. CROSBY REACTANCE TUBE MODULATION Filed Dec. 27, 1939 .2 Sheets-Sheet 1 AAAAIA VI CONTROL 52 M00- I um TING POTENTIALS AMPL/F/ERS ATTORNEY 60 r u J4 /M1/,LT/PL/ERS SOURCE 5 OF WA VE I I INVENTQR ENERGY MURRA 0 R085? April 7,1942. M. G. CROSBY 2,278,429

REACTANCE TUBE MODULATION Filed Dec. 27, 1939 2 Sheets-Sheet 2 SOURCE OF 3 OSC)/LLA 710M? l I I H "5 7 20 REA 07/ v5, "5

con/p201 POTENTIALS AMPLITUDE OSCILLAT/ON GENERATOR ZOQ R1 6P 1.. 3 5 REACT/V5 E I EFFECT R245 .B i E o' c I M0D.P07T +5 'BPC' T -INVENTOR MURRAY G. CROSBY ATTORNEY Patented Apr. 7, 1942 2,278,429 7 REACTANCE TUBE MODULATION Murray G. Crosby, River-head, N. Y.,. asslgnor to Radio Corporation of of Delaware America, a corporation Application December 27, 1939, Serial No. 311,074 14 Claims. (01. 119-1715) This application concerns new and improved reactance tube circuits of the nature of those described in my United States application #136,578, filed April 13, 193?, and in. my United States application #209,919, filed May 25, 1938,

now United States Patent No. 2,250,095, dated July 22, 1941. In the present application'a singlereactance' tube circuit is described which is well suited to operation on higher frequency waves.

A two-tube balanced reactance tube arrangement is also disclosed which is diflerentially modulated by the control potentials, but the scribed in the preceding paragraph.

In the balanced reactance tube circuit small linear reactive changes can be obtained with change of control potentials so that the said circuit may be used to control the tuning of a tuned circuit to accomplish phase modulation of wave energy thereon. My application also discloses new and improved phase and frequency modulation systems using the balanced reactance tube arrangement.

All of the modifications shown may be used in automatic frequency control circuits operating on a heterodyning oscillator in a receiver as well as in frequency or phase modulation circuits as disclosed in application #136,578, filed April 13, 1937.

In describing my invention in detail, reference will be made to the attached figures wherein:

Figure 1 illustrates an improved reactance tube circuit cooperating with .a source of modulating potentials and an electron coupled oscillation generator to modulate the frequency of operation of the latter.

Figure 2, which is a modification of Figure 1, uses two reactance tubes in a balanced circuit which has a stabilizing effect on the oscillation generator circuits. In this figure a novel frequency modulation system is also included.

Figure 3 and Figure 5 are modifications of the arrangement of Figure 2.

Figures 4, 5a and 5b are curves and graphs used to explain the operation of the reactance tube circuits, while Figure 2a illustrates the manner in which the two tube reactance arrangement is connected with 5 a tuned circuit excited by wave energy to control the tuning of the circuit and thereby phase modulate the wave energy in said circuit.

In my United States Patent No. 2,250,095, the principle of tuning the input circuits ofthe reactance tubes has been described in connection with Figure 3 of said application. The attached Figure 1 shows how this principle may be applied to a singletube and how capacitive coupling may be used in place of inductive coupling as used in said prior application.

In Figure 1, tube I, which is: the reactance tube, is of the pentode-tube type, and has its anode 2 coupled by a condenser 3 to a tuned circuit 5 comprising inductance L2 and capacity C2. The circuit 5 connects the grid 8, cathode l0, and screen grid I2 of an electron-coupled oscillator tube 20 in regenerative'circuits for the production of oscillations. The cathode 22 oi the reactance tube I is coupled to circuit 5 also so that the reactive effect produced in tube l is of the oscillation generation circuit 5. The control grid 24 of tube I is coupled to the circuit 5 by phase shifting condenser C and the tuned reactance comprising inductance Li and condenser Cl. Modulating or control potentials to control the reactive effect are supplied at 26 to the control grid 24.

Tube l is the reactance tube which produces the reactive effect in its plate circuit. The feedback phase shifter consists of capacitance C and tuned circuit Ll-Cl shunted by resistance R. That is, high frequency voltage from the circuits of tube 20 is supplied to the anode 2 of tube l and throughthe phase shifter circuit including C, Ll, Cl, and R to the grid of tube i. This phase shifter is of the constant-current type in which the reactance of the capacitance C is made large compared to the impedance of the tuned circuit Ll-Cl. The capacitive reactance, therefore, determines the phase of the current in the said circuit so that the potential drop across the resistive tuned circuit LI-Cl, which is resonated at the frequency for which the reactive effect is being obtained, takes the phase of the current and leads the plate voltage by practically Since the current pulses which reach the anode 2 lead the voltage on the said anode by about 90", a reactive effect is produced in the tube and this reactive efiect, which is in this case capacitive, is efiective in the circuit lit-C2 which controls the frequency of operation of the oscil. lation generator. The degree of reactive effect is controlled by the bias potentials on the grid 24. If the grid is made more positive the reac tive eifectincreases. If the grid becomes more negative the reactive eifect is decreased.

If the frequency range over which the reactance is to operate is large compared to the selectivity of circuit LI-CI, the damping effect of R may be increased by making R lower. If a smaller range of frequency control, but a high sensitivity to control potenial is desired, resistor R may be removed completely. Reducing the value of C increases the reactive efiect, but unless the reactance of C is made large compared to the impedance of the tuned circuit, a resistive effect is introduced in the variable reactance effect provided by the tube I.

Direct-current voltage is fed to the anode 2 of reactance tube I through radio-frequency choke RFC. This voltage may also be supplied by means of a direct connection to the oscillator tuned circuit L2-C2 if the oscillator tuned circuit is of the type which has the plate voltage on it. Capacitance 3 blocks the reactance tube plate voltage from the tuned circuit L2--C2 of the oscillator tube 20. The oscillator tube 20 is of the electron-coupled type which supplies its output from tuned circuit L3-C3 electronically coupled to the generating circuits and electrodes. Plate voltage is supplied by lead 23 to the anode 25 of tube 20. Voltage for the screen grid I2 of tube 20 is supplied from the plate source by means of potentiometer resistances 21 and 28. The oscillations generated and controlled as to frequency in accordance with control of the grid 24 of tube I is supplied throughcoupling con- .denser to any utilization means. The circuit if controlled at 24 and 26 by modulating potentials produces frequency modulated waves. If controlled by AFC potentials oscillations of substantially constant frequency are produced.

In the circuit of Figure 1, the feed-back capacitance C may be eliminated and inductive coupling effected between inductances LI and L2. This would make the circuit a single-tube equivalent of the circuit of Figure 3 of my United States Patent No. 2,250,095.

The circuit of Figure 2 shows a balanced type of reactance tube circuit which I have found to be very suitable for the production of oscillations of constant frequency due to advantages obtained by the balance. In my United States Patent No. 2,250,095, in Figure 3, I show a circuit employing this principle. In the circuit of said application I employ inductive coupling between the circuit to be tuned and the tuned circuit connected with the. reactance tube grids. In the circuit of Figure 2'of the present application capacitive coupling is employed between the plate and grid circuits of the reactance tube I' in the same manner as in Figure 1. However, Figure 2 differs from Figure 1 in that a second tube 52 is provided which gets on its grid 54 a feedback voltage 180 out of phase with the voltage on the grid 24 of tube I. That is, in the modification of Figure 2, the grid 24 derives a voltage through C of a particular phase while the grid 54 of tube 52 gets by way of the tuned circuit comprisinginductarice'56 and condenser 58 a voltage substantially 180 out of phase relative to the said voltage on grid 24. .That is, if we assume zero phase of the voltages on anode 2 the voltage impressed by C on grid 24 is shifted 90 while the voltage impressed on the grid 54 is shifted 180 more or 270 relative to the zero phase voltages on the anode 24 of tube I. Furthermore, if we look at the voltages on the anode 53 as being of zero phase, the voltage on the grid. 54 is displaced by so that the phase relation for the reactive effect is established.

It will be noted that voltage is fed back through capacitance C (which is the natural capacitance between the grid and plate of tube 52) tending to oppose that fed to circuit 56 by C. The opposition is caused by the fact that the voltage fed back by C is at-the opposite end of coil 55 which has the opposite polarity. This opposing feedback would completely neutralize the reactive eifect if C and C' were made equal. However, this equality is intentionally avoided by making C larger than C so that the predominate feed- .back is due to C. This causes the resulting voltage appearing on grid 54 to be out of phase with that fed to grid 24 since that voltage is predominantly fed from C through coil 56.

Since the tunedcircuit consisting of 55 and 58 is tuned to the frequency of the energy which is to be modulated, this circuit is resistive and, therefore, acts as though pure resistances were connected from grids 24 and 54 to ground. Hence capacity C in conjunction with this resistive effect forms the phase shifter which produces a 90 displaced voltage on grid 24. Capacity C is adjusted to be of high reactance compared to the resistive effect of 58 so that the current flowing is determined by the capacity and is, therefore, leading the applied voltage from the anode. The drop across the resistive effect of 58 to grid 24 will, therefore, be leading like the current in a condenser and when. this voltage is amplified through the tube, the current fiowing in the plate circuit of the tube is also leading and the reactive eifect is the sameas a condenser. The current flowing through the condenser C has thus been amplified by the tube so that the plate circuit of the tube presents a capacitive effect which is variable by the amount that the amplification of the tube is variable.

The voltage appearing on grid 54 of tube 52 is 180 out of phase with that appearing on the grid of tube I. This makes the voltage on 54 lagging with respect to the anode voltage. The

. tube then amplifies a current such as would flow through an inductance so that the reactive effect appearing in the plate of tube 52 is inductive and has an effect on tuning which is opposite to that of tube I. When these two opposing tuning effects produced by the two tubes are properly balanced, the advantages of stability as well as improved range and linearity of reactance variation are obtained. Thus, if variations in the direct-current supply potential to electrodes in the tubes causes variations in the current impulses, the resulting reactive changes are opposed and the total reactive efiect is balanced. This causes the tube I to produce a compensating capacitive reactance which neutralizes the inductive reactance of the tube'52 as long as the amplifications of the two tubes are balanced. As a consequence, in the absence of modulatingpotentials and in the presence of variations in power supply potentials on tube electrodes, my tube reactance circuit tends to stabilize the oscillation generator and compensate for said potential variations so that oscillations of substantially constant frequency are generated. Obviously, when the advantages gained by, the use of an electroncoupled oscillator are combined with the advantages gained by the use of my self-compensating reactive tube arrangement, oscillations of substantially constant frequency are obtained irrespective of variations in tube electrode voltages.

Diiferential modulation of tube electrode volthand, any cophasai modulation of the element.

voltages produces an effect in one tube which is compensated for by the other tube so that such undesirable variations are eliminated.

In the circuit of Figure 2, inductance 58 and split-stator condenser 58 are tuned to the frequency of the desired reactive effect. Here, they are tuned to substantially the mean frequency at which the oscillator is to operate. The reactive effect appears in the common plate circuit of the two tubes which may, asshown, be coupled by condenser 8 to the oscillator tuned circuit L2-C2 for frequency stabilization and/or frequency modulation. The reactance .eifects obtained by my invention may be applied to the tuned circuitof an amplifier and maintained under complete control of the modulating potentials. As a consequence, this arrangement is well adapted to use for phase modulation. For phase modulation the switch S is moved to contact PM so that the reactive efiect is now in parallel with the tuned circuit 60 in the output of a relay tube 6| connected with a source of wave energy as shown in Figure 2a. The reactive effects produced, as described above, phase modulate the wave energy amplified in SI and supplied to circuit 60.

Variable capacitance C is the feed-back coupling condenser which corresponds to condenser C in Figure 1.v This capacitance may be composed of the internal grid-to-plate capacitance of the tube together with added external capacitance, if necessary, or, as I have found, may consist of the unbalance between the grid-to-plate capacitances of the two tubes 2 and 52 and their wiring. Complete control of this capacitance is obtained when C is larger than the condenser C which may be connected between the grid 54 and plate 52 of the second tube so that the two may be relatively adjusted for'complete neutraliza-. tion or any degree 'of off-neutralization desired. The capacitance 0' usually is composed of the tube capacity only and for that reason is shown by dotted lines.

Diflerential modulation Is applied at 26 through transformer 85 to the screen grids 58 and 80 which are by-passed by condensers BPC. Potentiometer I59 allows a relative adjustment of the screen potentials so as to make up for tube differences and produce a completely balanced circuit. Modulation could be similarly applied to any other element voltage of the tubes.

In the circuit of Figure 2, the'split-stator con denser and two-terminal inductance I03 and I02 may be replaced by a mid-tapped coil and a twoterminal condenser, if those types of elements are preferred.

effect will be completely balanced out when the control potential is zero. When positive control potential is applied, the grid 54 of tube 52 is made more positive. This causes tube 52 to draw more cathode current, and, therefore, places both cathodes at a higher positive potential due to the potential drop in cathode resistance 'IIi shunted by by-pass condenser I2, This higher positive cathode potential is equivalent to -a higher negative potential onthe grid 24 of tube I. Thus, the required diiferential control of the gain of the tubes land 52 by the control potentials is obtained. The common cathode resistor IIIv causes the grid potential of the one tube to vary in the opposite direction to that of the other. However, this common cathode resistor I0 is not absolutely necessary because the circuit is differentially unbalanced by varying an element voltage of one tube, say 52, without varying that of the other tube, say I. ode resistor I! tends to increase the sensitivity to control potentials and increases the range of reactance variation obtainable.

The wave generator indicated by ablock diagram at 20' may be as illustrated in Figures 1 and 2 or of any type known in the art. The reactive efl'ect provided by the balanced arrangement comprising tubes I and 52 stabilizes the operation of the generator which may also be controlled by potentials at 20. A common directcurrent source ,or sources which vary in potential in synchronism supplies the generator and reactance tube arrangement.

Figure 5 is a circuit of the balanced type which uses phase shifters which are untuned. Thephase shifter for tube I consists of resistance RI and capacitance C2. RI is made large compared to the reactance of C2 so thatthe vector rela tions of the circuit are as shown in Figure 5a. In Figure 5a, E is the applied voltage which is supplied from the common plate circuits of tubes I and 52 and I is the current flowing in the phase shifter circuit RI, C2. RI is the voltage drop across resistor RI and XcI is the voltage drop across capacitance C2. The angle 0 between the appiied voltage E' and the drop across the capacitance C2, which is fed to the grid of tube I, is seen to be substantially and, more nearly approaches 90 as the ratio between RI and C2 is increased.

The phase shifter for tube 52 consists of capacitance C3 and resistor R2. In this case, the reactance of C3 is made large compared to resistance R2 so that the current is substantially reactive. The vector diagram for the phase shifter R2. C3 is shown in Figure 5b. It can be seen that th s type of phase shifter produces a phase shift 0' which is a' shift in the opposite direction to that effected by the other type of phase shifter in which the resistance is made large compared to the reactance. This makes the reactive effect of tube I opposite 'to that of tube 52 so that for the balanced condition the reactive effects cancel and differential modulation is required to produce the reactance change.

Differential modulation is accomplished in the circuit of Figure 5 by means of the push-pull feed from transformer 90 to the suppressor grids 9| and 92. Capacitances BPC are radio-frequency by-pass condensers and 84 is a blocking condenser. Resistor 86 furnishes a direct-current return for the grid 24' of tube I.

The reactive eiiect supplied to generator 20' stabilizes operation of the same whichthen may be controlled by potentials from 26. Direct-cur- The common cathrent voltages which vary similarly are used here as in the prior modifications.

In the circuit of Figure 5, capacitance C2 and C3 may be replaced by inductances of the same reactance and the same balance action will be obtained. In all of these balanced circuits there 1 are two methods by which the reactive effect of one tube may be balanced against that of the other so that element voltage supply variations will be neutralized. One of these methods is to balance the amount of voltage fed .back to each tube. This might be done by varying the relative capacities of the split-stator condenser 5c in Figure 2, by varying the relative sizes of the two halves of the inductance E5 in Figure 3, or by varying the values of RE, C2, and R2, C8, in Figure 5. in any of these cases the balance would be made by increasing the voltage fed back to the tube which did not produce a large enough reactive efiect. The second method of balance is by means of the screen-grid balancing potentiometer @Q as shown in Figure 2. In the case of Figure 5, it has been found convenient in practice to have both of these types of balance available and to do so 08 was made variable" and a screen-grid balancing potentiometer was included also.

I have found the balanced circuit of Figure 2 and Figure 5 to have many desirable features which make it highly practical. Operation of the balanced arrangement shown in Figure 2- with the reactive plate circuits connected across the oscillation circuit C2, L2 of an electron-coupled oscillator gave the following results: With the reactance tube arrangement disconnected by opening switch S, the frequency of the electroncoupled oscillator 20 could be made almost independent of the plate supply variations by varying the voltage on the screen electrode 23. The single plate supply was common to all tubes.

' When the reactance tube was placed across the circuit, I found that adjustment of potentiom eter 69 effected a complete elimination of the small amount of frequency change due to plate supply variations to the electrode 25. which the electron-coupledv oscillator had operating alone.

By complete elimination, I mean a flat frequency versus supply voltage characteristic for voltages down to near the point where oscillations cease.

At the very low voltages all oscillators seem to vary quite widely with plate voltage.

The stabilization of the mean frequency is obtained due to the operation of two effects in the double reactance tube circuits. First, the addition of the second reactance tube balances out A the reactance variations in the reactance tube circuit which are due to the power supply variamerits and has a more desirable characteristic. D

In Figure 4, curve A shows how the usual singletube reactance tube effect varies in amplitude with variations in frequency of the voltages producing the-reactive effect. Curve B shows the smacac type of variation obtained with the balanced circuit. There seems to be negative resistance introduced on either side of the mean frequency instead of negative on one side and positive on the other, as in curve A. This greatly reduces the amount of variation and, also, produces a characteristic which is very valuable in producing phase modulation by modulating the tuning of a tuned amplifier, as illustrated in Figure 10.. Since the amplitude of the impedance is raised on either side of the mid-frequency, the inherent selectivity of the modulated tuned circuit is compensated for so that greater degrees of phase modulation may be realized for a given degree of concomitant amplitude modulation.

Aside from utilizing this balance feature to improve the stability and reduce the concomitant amplitude modulation of frequency modulated oscillators, I may also use it to great advantage as the reactance tube for the automatic frequency control in the carrier-exalted receivers. In some instances, such receivers are troubled by motorboating due to the audio circuits feeding back so as to vary the frequency of the automatically controlled oscillator. Since the stability of this oscillator is practically turned over to the reactance tube which has its reactance directly dependent upon element voltages, and since the frequency discriminator circuit is the very sharp carrier filter, this motorboating effect is very pronounced. Even a voltage-regulated power supplyv does not completely remove the tendency and it become." necessary to resort to a somewhat reduced sensitivity of the automatic frequency control. This balanced circuit will completely remove that effect and allow a greater degree of automatic frequency control.

What is claimed is:

1. In a wave generating system an electron discharge tube having a plurality of electrodes connected in oscillation generating circuits including a reactance, a source of direct-current potentials for energizing said electrodes by direct-current potentials whereby oscillations are generated'in said circuits, and means for maintaining the frequency of operation of said oscillation generator substantially constant irrespective of variations in tube electrode energization voltages comprising, a pair of electron discharge devices each having an electron receiving electrode. a cathode and a grid electrode, means connecting corresponding electrodes of said devices to said source '0! direct-current potential, means coupling the impedance between a pair of electrodes in each of said devices in shunt to reactance of said oscillation generating circuits, and means for impressing phase displaced oscillations from said oscillation generating circuits on two electrodes in each of said devices to produce in said devices opposed reactive effects which vary in phase with variations in the direct current potential of said source and are added to the reactance in said generating circuits said last named means comprising a connector connecting the electron receiving electrodes of said devices together and to a point on said generator circuits, a plurality of reactances in a series connection between the electron receiving electrode of one of said devices and the grid of the other of said devices and a connection between said series connection and the grid of said one of said devices.

2. In a wave generating system an electron discharge tube havlng a plurality of electrodes connected in oscillation generating circuits including a reactance, a source of direct-current potential connected with said electrodes whereby oscillations are generated in said circuits, and means tion generating circuits, and'reactance means for impressing phase displaced oscillations from said oscillation generating circuit in two electrodes on each of said devices to produce in said devices opposed reactive effects which are combined in variabl amounts which change with variations in the direct current potential applied to said like electrodes of said devices and are added to the reactance in said generating circuits to stabilize the operation thereof, said reactance means comprising a parallel circuit coupled between corresponding electrodes of said devices and tuned to the frequency of the generated oscillations. I

3. In a wave generating system an electron discharge tube having an output electrode and a plurality of electrodes connected in oscillation generating circuits including a reactance, a source of direct-current potential for energizing said electrodes by direct-current potentials whereby oscillations are generated in said circuits, an output circuit connected to said output electrode and coupled to said generating circuits by the electron stream only of the tube, and means for maintaining the frequency of operation of said oscillation generator substantially constant irrespective of variations in tube electrode direct-current potential comprising, a pair of electron discharge devices each having a plurality of electrodes, means for applying directcurrent potentials from said source to corresponding electrodes in said devices, means coupling the impedance between a pair of electrodes in each of said devices in parallel and in shunt to reactance of, said oscillation generator circuits,

and means for impressing phase displaced oscillations from said oscillation generating circuits on two electrodes in each of said devices to produce in said devices reactive effects which vary with variations in the direct current potential of said source and which are added to the reactance in said generating circuits, said last named means comprising an inductance and a condenser connected in parallel and tuned to the frequency of operation of said generating circuits, couplings between opposite ends of said parallel connection and corresponding electrodes in said devices and a coupling between one end of said parallel connection and another electrode in one of said devices.

4. Apparatus as recited in claim 1 wherein one of said reactive effects is capacitive-the other inductive, and wherein means is provided to vary said produced reactive effects in phase opposition by modulating potentials to modulate the frequency of the wave generated by said generator.

5. In a frequency modulation system, a stabilized generator as recited in claim. 2, a source of signal potentials and means connecting said,

source of signal potentials in phase opposition to corresponding electrodes in said devices to control said produced reactive effects at signal frequency to frequency modulate the generated oscillations.

6. In a frequency modulation system, a system as recited in claim 3 wherein one of said reactive effects is capacitive, the other inductive, a source of signal potentials and means controlled by said signal potentials and operatively associated with correspondingelectrodes in said devices for varying said inductive and capacitive reactance effects in phase opposition at signal frequency to frequency modulate the oscillations enerated. 1

7. In a wave generating system, an electron discharge tube having a plurality of electrodes connected in regenerative oscillation producing circuits including reactances, means for impressing direct-current potentials .on the electrodes of said tube whereby oscillations are produced in.

said tube and circuits, and means for maintaining the frequency of operation of the oscillations substantially constant irrespective of variations in the applied direct-current potentials comprising, a pair of electron discharge devices each having an anode, a cathode, a control grid, and an additional grid, means coupling the impedance between the anode and cathode of each of said devices in parallel and in shunt to the reactance in said regenerative circuits, means for impressing voltages in phase displaced relation from said generating circuit on the anode and control grid in each of said devices, and means for impressing direct-current potentials of relatively adjustable value from said first named source on the additional grids of said devices.

8. In a wave generating system, an electron discharge tube having a plurality of electrodes connected in regenerative oscillation producing circuits including, rea'ctance, meansfor impressing direct-current potentials on the electrodes of said tube whereby oscillations are produced in said tube and circuits, and means for maintaining the frequency of operation of the oscillations substantially constant irrespective of variations in the applied direct-current potentials comprising, a pair of electron discharge devices each having a plurality of electrodes, including an anode, and a control grid, means coupling the impedances between a pair of electrodes in each of said devices in shunt to the reactance in said regenerative circuits, means for impressing voltages from said generating circuit on the anodes of said devices, a coupling between the anode of one deviceand the control grid of said one device, a circuit tuned to the frequency of operation of said generator'connected between the control grids of said devices, and means for impressing direct-current potentials which vary in a manner similar to variations 'in the direct-current potential supplied to said electrodes of said tube on corresponding electrodes of said devices.

9. In a wave generating and frequency modulating system, an electron discharge tube having a plurality of electrodes connected in regenerative oscillation producing circuits, means for impressing direct-current potentials on the'electrodes of said tube whereby oscillations are produced in said tube and circuits, and means for maintaining the frequency of operation of the oscillator substantially constant irrespective of variations in the applied direct-current potentials comprising, a pair of electron discharge devices eachhaving a plurality of electrodes, means coupling the impedances between apair of electrodes in each of said devices in parallel and in shunt to the reactance in said regenerative circults, means for impressing voltages in phase displaced relation from said generating circuit on a pair of electrodes in each of said devices, means for impressing direct-current potentials of relatively adjustable value, which potentials vary in a manner similar to variations in said directcurrent potentials impressed on said tube electrodes, on electrodes of said devices, and means for modulating the impedances of said devices in phase opposition by signal potentials,

10. A variable balanced reactance comprising, a pair of electron discharge tubes of the multipleelectrode type, means for applying alternatingcurrent voltages to corresponding electrodes of saidtubes, a phase shifting circuit coupling one of said corresponding electrodes oi one of said tubes to another electrode of said one tube, a circuit parallel-tuned to the ire uency of said alternating-current potentials connecting said other electrode of said one tube to an electrode lating system, an electron discharge tubehaving a cathode, a plurality of grid like electrodes and an output electrode, oscillation generating circuits including reactance coupling said grid like electrodes and cathode in oscillation generating circuits, an output circuit coupled to said output electrode, said output electrode and circuitbeing coupled tosald oscillation generation circuits substantially by the electron stream only of the tube, means for maintaining the frequency of operation of the oscillation generator substantially constant comprising a pair of electron discharge devices each having, a plurality of electrodes, means coupling the impedances between a pair of electrodes in each of said devices in par allel and in shunt to reactance of said oscillation generator circuits, means for impressing relatively adjustable potential which vary in value in a similar manner on electrodes in said tube and devices, means for impressing phase displaced oscillations from said oscillation generating circuits on two electrodes of each of said devices, and means for impressing modulating potentials 'in phase opposition on electrodes in each of said devices. I

12. In means for wave length modulating wave energy, an electron discharge tube having electrodes connected with a. source of direct-current potential and with a tuned circuit having reacance which determines the wave length of the wave energy flowing in the circuit, the reactance of said circuit including a, component which may vary with variations of said direct-current potential, and means producing an inductive reactive eflect and a'capacitive reactance efiect, which effects vary simultaneously in accordance with signals and in accordance with changes in said direct current potential, means for combining the said effects in sucha manner that the variations due to signals add andthose due to changes in direct-current potential oppose, means for unbalancing said reactive effects so that those due to changes in direct-current potential are unequal and provide a resultant which opposes the variations in the reactance of said circuit due to pair of electrodes in each of said devices to said tuned circuit whereby oscillations therefrom are impressed in phase displaced relation between a pair of electrodes in each of said devices to proreactive efiect included in said tuned circuit and consequently vary the phase of the oscillations set up therein.

14. In combination, an alternating current circuit across which a variable reactance is to be developed, a pair of electron discharge device systems each having an anode, a cathode, and a grid, the anodes of said systems being connected together and to said alternating current circuit, the cathodes of said systems being connected together and to said alternating current circuit, a circuit parallel tuned substantially to the frequency of operation of said alternating current circuit connected between the grids of said systems, a condenser connected between the anode and grid of 'one of said systems, said condenser and parallel tuned circuit operating to impress voltages on said grids which are substantially in phase opposition with respect to each other and substantially in phase quadrature with respect to the voltage across said alternating current circuit, and means to oppositely vary the conductivities of said electron discharge device systems to vary-the amount of the reactance effectively connected in shunt to said alternating current circuit.

MURRAY G. CROSBY. 

